heteroprio: simplify code by using starpu's functions and correct mistakes

3 jobs for !27 with update/auto-heteroprio in 19 minutes and 43 seconds (queued for 3 seconds)
latest detached
Status Name Job ID Coverage
  Build
passed build #1226938

00:05:38

 
  Deploy
passed check #1226939

00:10:15

passed simgrid #1226940

00:03:49